1. Field of the Invention
The present invention relates to a keyboard assembly having an improved waterproof structure of a torsion bar receiving portion in each key switch provided with the torsion bar.
2. Description of the Related Art
On a keyboard of a computer or a word processor are arranged a large number of key switches 100, for example like a keyboard B shown in FIG. 7. Key tops are attached respectively to the key switches 100 so as to be pushed by a user's finger. The key tops are in various planar shapes, including a generally square shape, a half-cut shape thereof, a sideways long shape, and a deformed L shape.
As shown in FIG. 8, the key switches are each generally composed of a key top 110 and a key switch body 120. The key top 110 comprises a top plate 111 to be pushed with a finger, a cylindrical stem portion 112 extending downward through an axis X of the key top from a lower surface of the top plate 111, pawl portions 113 formed downwards on both sides of the stem portion 112, and a skirt wall 114 extending downward from a peripheral edge portion of the top plate 111.
The key switch body 120 comprises a housing 121 which houses the key switch body 120 therein, an inverted bowl-shaped rubber spring 122 connected to a lower end of the stem portion 112, and a membrane switch 124 disposed below a convex-shaped pressing portion 123 which is formed centrally downward from a top part of the rubber spring 122. The housing 121 is formed with a cylindrical socket 125 into which the stem portion 112 is inserted vertically slidably and is also formed with pawl engaging holes 126 for engagement with the pawl portions 113 to prevent extraction of the key top 110 from the key switch body 112.
In the key switch of the above configuration, when the top plate 111 of the key top is pushed by a user's finger, as shown in FIG. 9, the stem portion 112 slides downwards through the socket 125 and a lower end thereof pushes the rubber spring 122 downward, causing the rubber spring to buckle. As a result, the pressing portion 123 of the rubber spring pushes the membrane switch 124 and causes the membrane switch to turn conductive. Upon release of the user's finger from the top plate 111, the key top 110 reverts to its original position with a repulsive force of the rubber switch 122, so that the membrane switch 124 turns OFF.
In each of the switches 100 of the above keyboard, key tops 110A of such keys as shift key, space key, and tab key are each provided with a sideways long top plate 111 as in FIG. 10, but the shape, position and size of the stem portion 112 are set equal to those in a sectional key switch structure shown in FIG. 8. Therefore, what is called a torsion bar, as a spring member, is incorporated in the key top so that the top plate 111 can be smoothly depressed right beneath even when it is depressed on an end side thereof.
The torsion bar, indicated at 130, comprises a body portion 130a which is in a rectilinear shape and hook portions 130b extending in an inward L shape from both ends of the body portion. The body portion 130a is fitted in and engaged with support members 129 formed on the back side of the top plate 111 and is thus retained on the back side of the top plate. A pair of post-like support projections 131 of a hollow structure are erected on both sides of the housing 121, with support holes 131a being formed in upper portions of the support projections 131, respectively. The hook portions 130b of the torsion bar 130 are engaged respectively in the support holes 131a, whereby the torsion bar 130 is locked. With the torsion bar 130 thus locked, the stem portion 112 is inserted into the socket 125. In this way the key tops 110A of such keys as shift key, space key, and tab key are mounted onto the keyboard.
Drink cans or cups or the like may be placed on a table around the keyboard of this type and therefore it is considered preferable for the keyboard to have a waterproof structure.
Reference will now be made to a water entry route for an electric circuit portion of each membrane switch 124 in the interior of the keyboard. In each key switch 100 of the structure shown in FIGS. 8 and 9, water may enter the interior of the keyboard through the opening portions of the socket 125 and the pawl engaging holes 126. However, since those opening portions are covered with the skirt wall 114 of the key top 110, it is considered that a high waterproofness is ensured.
However, in the key top 110A of, for example, a shift key or a space key having the torsion bar 130 shown in FIG. 10, the retaining holes 131a formed in the support projections 131 for retaining the hook portions 130b of the torsion bar 130 are positioned on end sides of the key top 110A, so the opening portions of the retaining holes 131a may be a cause of water entry. In more particular terms, the support projections 131 are of a hollow structure and an electric circuit which constitutes the membrane switch 124 is provided below the support projections 131, therefore, if water should enter the interior through the retaining holes 131a of the support projections 131, there is a fear that the electric circuit of the membrane switch 124 may be corroded or damaged.
If the support projections 131 are formed not as a hollow structure but as a solid post-like structure and if bent portions for retaining the hook portions 130b of the torsion bar 130 are formed on end sides of the support projections respectively, it is required that the support projections 131 be formed in L shape. However, in forming the keyboard by molding a resin, if a plurality of solid L-shaped structures are erected about a housing plate in the keyboard, there arises the problem that the shape of a mold for molding the keyboard housing plate becomes complicated. More particularly, in the structures shown in FIGS. 8, 9 and 10, the portion of the socket 125, the portion of each pawl engaging hole 126, and the portion of each support projection 131 are each of a vertically through structure, so it is easy to design a mold in case of molding the keyboard assembly with use of both upper and lower mold halves, but if a structure having L-shaped support members not of a through structure on an upper surface of the housing plate is to be formed by molding with use of upper and lower mold halves, the mold becomes complicated in shape and difficult to design.